1. Field of the Invention
This invention relates to a radiation detector having a scintillator, a light guide, and a photomultiplier tube optically coupled in turn, and tomography equipment provided therewith.
2. Description of Related Art
This type of radiation detector is used in emission computed tomography (ECT: Emission Computed Tomography) equipment to detect radiation (such as gamma rays) emitted from radiopharmaceutical that is administered to a subject and is localized to a site of interest for obtaining sectional images of the site of interest in the subject showing radiopharmaceutical distributions. Typical ECT equipment includes, for example, a PET (Positoron Emission Tomography) device and an SPECT (Single Photon Emission Computed Tomography) device. A PET device will be described by way of example. When examinations are performed through a PET device provided with the foregoing radiation detector, radiopharmaceutical labeled with positron emitting nuclides is firstly administered to a subject by injection. The positron emitting nuclides undergo β+ decay within the subject to produce positrons. The positrons immediately collide with electrons in the subject to annihilate, and simultaneously to produce a pair of gamma rays (an annihilation gamma ray-pair) that travels in opposite directions to each other. The PET device obtains sectional images showing radiopharmaceutical distributions in the subject through coincidence of the annihilation gamma ray-pairs with a detector ring.
Such radiation detector arranged in the detector ring of the PET device is often equipped that is capable of position discrimination in a depth direction of a scintillator provided in the radiation detector for improved resolution. Particularly, such radiation detector is used, for example, in a PET device set for animals. FIG. 15 is a perspective view showing a construction of a conventional radiation detector. Such radiation detector 50 is composed of scintillation counter crystal layers 52A, 52B, 52C, and 52D in which scintillation counter crystals 51 of parallelepiped are accumulated in two dimensions, and a photomultiplier tube (PMT) 53 having a function of position discrimination that detects fluorescence irradiated from each of the scintillation counter crystal layers 52A, 52B, 52C, and 52D. Here, each of the scintillation counter crystal layers 52A, 52B, 52C, and 52D is laminated in a z-direction to form a scintillator 52 that converts incident radiation into fluorescence.
As noted above, four scintillation counter crystals are provided for performing more correct position discrimination in a depth direction of the scintillator 52 (a z-direction.) Providing of multiple scintillation counter crystal layers may realize discrimination of an incident position of gamma rays in the scintillation counter crystal layers in the z-direction. Consequently, a discriminative capability of the incident position of gamma rays may be enhanced (see, for example, Patent Literature 1.)
Two or more reflectors 54 are provided in each of the scintillation counter crystal layers 52A, 52B, 52C, and 52D. The reflectors 54 are arranged so as to be inserted between the scintillation counter crystals 51 that forms each of the scintillation counter crystal layers 52A, 52B, 52C, and 52D for reflecting fluorescence produced by the scintillation counter crystals. The reflector 54 does not surround each scintillation counter crystal 51from every direction, but is provided on two adjacent surfaces of the scintillation counter crystal 51 (see, for example, Patent Literature 1.) Such a construction allows position discrimination in the depth direction of the scintillator crystal layers.
[Patent Literature 1]
Japanese Patent Publication No. 2004-279057